Prosecutors on Thursday demanded a 25-year prison term for a woman at the center of a corruption scandal that led to the ousting of former President Park Geun-hye early this year.

Choi Soon-sil, 61, Park's longtime friend and confidante, was arrested and indicted in November last year on 18 charges, including abuse of power, coercion and bribery.

Special Counsel Park Young-soo and state prosecutors also demanded the court order her to pay a fine of 118.5 billion won (US$109 million) and forfeit 7.7 billion won.

She is suspected of illegally interfering in state affairs and colluding with the former president to pressure 50 conglomerates to donate 77.4 billion won to two foundations Choi allegedly controlled.

For An Chong-bum, Park's senior presidential secretary of policy coordination, the prosecution demanded six years in prison and a fine of 100 million won. He allegedly collaborated with Choi to force the corporate donations and took kickbacks from a local plastic surgeon accused of illegal treatment of Park.

The prosecutors also requested a four-year jail term for Shin Dong-bin, the chairman of retail conglomerate Lotte Group, on charges of bribing Choi with 7 billion won in addition to the group's donation to the non-profit organizations. They demanded he forfeit 7 billion won.

The prosecution said that Choi deserves a heavy punishment because she undermined Constitutional values by seeking personal gain by taking advantage of her ties with the president.

"The true nature of this case is the clandestine and unethical backscratching between political and money powers, and the greed and misdeeds of someone behind the curtain fully capitalizing on it," it said in its closing statement.

The prosecution slammed her for being the "culprit who threw the nation into confusion and turmoil, which eventually brought about the impeachment of a president."

Choi pleaded not guilty in her final statement.

"I have never once pursued any personal gains. And yet (the request for) slapping me with more than 100 billion won in fines makes me feel like I live in a country worse than a socialist state."

She also said that she respects Park and feels sorry for having caused trouble for her and the general public.

"I have stood by her for the last 40 years because I admire her strong side as someone who overcame all the suffering she experienced when she was young," Choi said, sobbing. "Looking back, I regret that I didn't leave her when she became president and it agonizes me even now."

Lee Kyung-jae, Choi's defense lawyer, said the 25-year imprisonment "was as good as dying in prison," accusing the prosecution of incriminating Choi in a politically motivated case.

This photo taken Dec. 14, 2017, shows Choi Soon-sil, a longtime friend and confidante of ex-President Park Geun-hye, entering the Seoul Central District Court to attend her corruption trial. (Yonhap)

"The majority faction in parliament that passed the impeachment motion has branded this case as an influence-peddling scandal and the prosecutors and special counsel have framed former president Park and my client as corrupt offenders," he said. "It's a miracle that my client has put up with the trial while keeping her sanity."

While Lee was making his closing arguments, Choi requested the judge allow a recess. As she moved to the defendant's waiting room, she screamed in apparent rage, before being taken outside in a wheelchair by guards.

The court is expected to deliver the ruling on Choi and the two other defendants on Jan. 26. (Yonhap)